Electric discharge apparatus



W. J. SCOTT ELECTRIC DISCHARGE APPARATUS Sept. 15, 1942.

Filed 001:. l, 1940 Inventor: William J. Scott,

His Attorney.

Patented Sept. 15, 1942 v 2,296,062 ELECTRIC mscnaaas arraaa'rus William J. Scott, Rugby, England, assignor to General Electric Company, a corporation of New York Application Octoberl, 1940, Serial No. 359,253 In Great Britain March 19, 1940 '1 Claims.

My invention relates to electric discharge apparatus including a discharge device having spaced electrodes, at least one of which is arranged in be directly heated by the passage of current therethrough for initially raising its temperature. with a common circuit arrangement wherein the operating current for such a'device is supplied to an electrode by a connection with one terminal only thereof it has been found that because of the resistance of the electrode there has been an objectionably unequal distribution of the operating current therein so that substantially only that half of the electrode adjacent said connecting terminal is effective as a cathode.

It is the object of my invention to provide improved electric discharge apparatus of the abovementioned character which includes thermally responsive switching means to provide for an initial electrode heating at the time of starting and to avoid the above-mentioned unequal distribution of the operating current in an electrode or electrodes during the normal operation of the device.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram illustrating one embodiment of my invention and Fig. 2 is a similar diagram illustrating a modification.

In the drawing, l is an electric discharge device which for example may be a discharge lamp of the positive column type comprising the-envelope 2 of tubular form which may contain a suitable gas or vapor as for example mercury vapor under low pressure. Arranged at opposite ends of the envelope are the electrodes 9 and 4 which are represented as being filamentary in form and preferably are coated with a suitable electron emissive material. If desired, the inner surface of the envelope may be covered with a suitable phosphor to produce a. fluorescent effect. One end of each electrode, the bottom end, as shown in the drawing, is connected with one side of the source 5 of alternating current cycle, 115 volt, lighting circuit. In one of these connections I have shown the control switch 6 and the ballast reactor 1.

Inasmuch as the device I has a starting voltage which is somewhat higher than the voltage of the source of supply and since it is desirable initially to raise the electrodes to an electron emitting temperature before the discharge is started, I have provided auxiliary switching apparatus which will cause the electrodes to become heated to an electron emitting tem-perature before the starting voltage is applied across the device. This switching apparatus also functions after the device has been started to correct the objectionable inequality of current distribution in the electrodes referred to above. The switching apparatus, which is heat responsive, is shown enclosed in the sealed envelope 9 which contains a suitable gas for supporting a glow discharge between the electrodes 9 and III, therein. The spacing of the electrodes and the gas pressure being such that at a voltage only a little lower than the line voltage a glow discharge occurs but does not occur at the are drop voltage of the device. The electrodes 9 and I0 are bimetallic strips each secured at its lower end in the press of the envelope and having contact points arranged on opposite sides at their upper or free ends. The strips 9 and III are preferably coated with electron emissive material and are so arranged that in response to an increase in temperature their free ends bend tow rd each other. Strip 9 connects with the other or upper end of the electrode 3 and strip I0 connects with the other or upper end of the electrode 4 whereby when the strips become heated by a glow discharge therebetween their resulting warping into contact with each other will short circuit the gap in which the glow discharge occurs and provide a low resistance path through which heating current may flow through the electrodes quickly to raise their temperature to that required for electron emission. Arranged on the opposite sides of the strips 9 and I0 are the back contact members ll and I! which have their lower ends embedded inthe press and have contact points at their'upper ends arranged to engage the adjacent contact points on the strips 9 and I 0 the supply which for example may be an ordinary 60 --with the back contact l2.

adjustment being such that when the auxiliary apparatus is not heated or at normal temperature the strip 9 electrically connects with the back contact II and strip to electrically connects These back contacts connect with the lower ends of the electrodes 3 and 4 respectively whereby in the normal or unheated condition of the auxiliary apparatus each electrode 3 and l is short circuited.

.The operation of the apparatus, briefly, is as follows: When the control switch 6 is initially closed the voltage applied to the strips 9 and I0 is sumcient to cause a glow discharge to be produced therebetween. The heat from this discharge soon warps the strips 9 and I0 causing them to engage each other thus short circuiting the glow discharge path and providing a. low

' resistance path through the electrodes 3 and 4 applied to the strips 9 and it drops to the arc drop voltage or the device which is insufilcient to support a glow discharge between the two strips. As the strips continue to cool they finally make contact with the back contacts ii and I2 and in so doing short circuit the electrodes 3 and 4. Thereafter, it will be seen that the operating current of the device I is supplied to both ends of each electrode I and 4 thus avoiding the objectionable inequality of current distribution in the electrodes.

The modified form of my invention shown by Fig. 2 is adapted for use when the discharge device is operated over a source of direct current supply. In this case the electrodes of the device may comprise a heated electrode such as shown at 3', which is the cathode, at one end only of the device, the electrode H at the other end being always an anode. The ballast in this case is represented as the resistor IS. The auxiliary switching device may comprise the single bimetallic strip 9', which is similar to the strip I of Fig. 1, and the electrode it between which the glow discharge is adapted to take place. The

back contact member ii is similar to the back contact ii of Fig. 1. The connections between the auxiliary apparatus and the discharge device i' are similar to those shown in Fig. 1 except that the electrode H has but one connection with the auxiliary device, namely, with the electrode it.

The operation of this form of my invention is similar to that oi! the form shown by Fig. 1, that is, when the switch 5 is closed a glow discharge takes place between the members 9' and it. The resulting heat causes the strip to bend to the right engaging the strip I! and closing the low resistance heating circuit through the electrode 3. The subsequent opening of the' heating circuit by the cooling of the strip I causes a discharge in the device i to start. After further cooling of the strip it engages the back contact ii thereby short circuiting the electrode 1'.

While I have shown and described the bimetallic strips 9 and il in the case of Fig. 1 and the strip 8' in the case of Fig. 2 as heated by a glow discharge, it is obvious that if desired the necessary heat may be supplied to these members from a resistor heater which in the case of Fig. 1 would be connected between the strips 9 and II and in Fig. 2 would be connected between the members 9' and I6. I prefer, however, to produce the heat for the operation of the thermal switch by means of a glow discharge within the envelope of the auxiliary apparatus as shown.

What I claim as new and desire .to secure by Letters Patent 0! the United States is:

1. In combination, an electric discharge device having spaced electrodes, one of which has an appreciable amount of resistance, means for connecting said electrodes with a source of current supply to energize the device, heat responsive means for closing a circuit across said device and including said one electrode in series to eilect an initial heating thereof, and means controlled by said heat responsive means for short circuiting said one electrode after the discharge has started in said device.

2. In combination, an electric discharge device having spaced electrodes, one oi which has an appreciable amount of resistance, means for connecting said electrodes with a source of current supply to energize the device and a switch having necting said electrodeswith a source of current supply to energize the device, other spaced electrodes each connected with one or said electrodes and between which a glow discharge is adapted to take place,switching means responsive to heat produced by said glow discharge ior producing a short circuit across said device and including said one electrode in series, and switching means responsive to a reduction in said heat incident to'the starting oi the discharge in said device for short circuiting said one electrode.

4. In combination. an electric discharge device having spaced filamentary electrodes, means for connecting said device with a source or currmt supply to energize the device, glow switch means for closing a circuit across said device and including said electrodes in series to eflect the initial heating thereoi and means controlled by said switch for short circuiting each of said electrodes after the discharge has started in said device.

5. In combination, an electric discharge device having spaced filamentary electrodes, means for connecting said device with a source of current supply to energize the device, an auxiliary electric discharge device having spaced electrodes connected to shunt said main device and between which a glow discharge is adapted to be produced prior to starting of the main device, switching means responsive to heat produced by said glow for closing a circuit across said main device and including said electrodes in series and switching means responsive to the extinction of said glow for short circuiting each of said electrodes.

6. In combination, an electric discharge device having spaced filamentary electrodes, means for connecting one end of each of said electrodes with a source of current supply to energize the device, a combined auxiliary electric discharge device and switch having a pair of spaced bimetallic switch members each connected with an opposite end of said electrodes and between which a glow discharge will occur before the discharge occurs in the main device, said members being constructed to warp toward and make connection with each other in response to heat roduced by said glow discharge, and a contact at the outer side of each of said members arranged to be engaged thereby during the normal operation of the device and connected with said one end of each of said electrodes.

7. In combination. an electric discharge device having spaced filamentary electrodes, means for connecting one end of each 0! said electrodes with a source 0! current supply to energize the device, and a switch having a plurality of thermally responsive elements arranged to engage each other when heated and connected each to one end of said electrodes at its opposite end, said switch having contacts each connected with an electrode at its said one end and each arranged to be engaged by a separate one of said elements when it is cool thereby short-circuiting the electrodes.

WILLIAM J. SCO'I'I. 

